[sarcmembers] Re: IC-736 and the TE Systems amplifier...
- From: "Bill McMillan" <12647@xxxxxxxxxxx>
- To: <sarcmembers@xxxxxxxxxxxxx>
- Date: Mon, 18 Jan 2010 18:58:23 -0800
I will donate the money for one Transistor ($50.00)
Bill McMillan
KI6LXV
-----Original Message-----
From: sarcmembers-bounce@xxxxxxxxxxxxx
[mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of John Maetta
Sent: Monday, January 18, 2010 5:59 PM
To: sarcmembers@xxxxxxxxxxxxx
Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...
So, how am I to proceed? Do I purchase the component or will the club?
John
N6VMO
----- Original Message -----
From: "Avery Wright KD4GBA" <kd4gba@xxxxxxx>
To: <sarcmembers@xxxxxxxxxxxxx>
Sent: Sunday, January 17, 2010 16:34 PM
Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...
> UPDATE:
>
> American MicroSemi has the MRF-247 in stock and on sale for $49.94 each.
> You can find it here:
>
http://store.americanmicrosemiconductor.com/mrf247.html?gclid=CM_h-7_XrJ8CFR
> D7agod1Bfl0w
>
> Avery
>
> -----Original Message-----
> From: sarcmembers-bounce@xxxxxxxxxxxxx
> [mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of Eric Lemmon
> Sent: Sunday, January 17, 2010 4:29 PM
> To: sarcmembers@xxxxxxxxxxxxx
> Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...
>
> John,
>
> I checked with several suppliers, including RF Parts, and could not find
> one
> that stocks the MRF-247. Since I assume(?) that the amplifier has four
> 75-watt transistors in parallel, it seems prudent to use a genuine MRF-247
> transistor for replacement, if one can be found. If a substitute
> transistor
> is used, such as the 2SC2782 or NTE478, it might be advisable to replace
> all
> four transistors to avoid mismatching issues.
>
> Since the 2SC2782 costs about $32 each, this is a significant expense. I
> hope we can find an MRF-247 rather than risking further damage with a
> mismatched component. Is TE Systems still in business?
>
> 73, Eric Lemmon WB6FLY
>
>
> -----Original Message-----
> From: sarcmembers-bounce@xxxxxxxxxxxxx
> [mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of John Maetta
> Sent: Sunday, January 17, 2010 3:24 PM
> To: sarcmembers@xxxxxxxxxxxxx
> Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...
>
> Today is a great day to keep dry, listen to the 40 meter swap net on
> 7.240MHz and work on radio gear.
>
> I opened the TE Systems amp and discovered the T/R and RF Sense relays and
> circuits are working, but the amp continues to draw 15amps after PTT is
> removed. The o'scope then revealed that the amp starts to oscillate when
> PTT is asserted and will not stop oscillating until power is removed. The
> amp has turned itself into a 100W noise generator.
> The noise emitted by the oscillations drowns out the swap net. :)
>
> Troubleshooting detected that one of the four MRF-247 final transistors,
> Q3,
> is the culprit. With Q3 disabled, the amp keys, draws 2 amps bias current
> and then current drops to ~0 when PTT is removed, just like it is supposed
> to.
>
> If any of you have one in your junk box, please let me know. Or we can
> order one.
>
> Here is what we need to repair the amp:
> http://www.datasheetcatalog.org/datasheet/motorola/MRF247.pdf
>
> I also need some wide solder wick (1/4" or wider) to help remove the
> transistor from the amp. All I have is the narrow wick.
>
> The other option is to leave Q3 disabled and run the amp at reduced power
> out.
>
> 73
>
> John
> N6VMO
>
>
>
>
> ----- Original Message -----
> From: John Maetta <mailto:j.maetta@xxxxxxxxxxx>
> To: sarcmembers@xxxxxxxxxxxxx
> Sent: Sunday, January 17, 2010 12:05 PM
> Subject: [sarcmembers] IC-736 and the TE Systems amplifier...
>
>
> Hello,
>
> Last week a member asked me to have a look at the IC-736 and TE
> System 2 meter amplifier. It was reported that the antenna(s) were
> exhibiting a high SWR and the TE Systems amp would constantly draw 15amps
> from the Astron power supply after the PTT was released.
>
> This morning I noted the following:
>
> A quick check of the setup found the IC-736 and amplifier are
> currently connected to the 2 meter AZ/EL antenna 'A' via the MFJ-864
> SWR/Watt Meter.
> Using the IC-736 only and running 25 watts output, I noted antenna
> 'A' is also displaying >3:1 SWR on the MFJ-864 SWR/Wattmeter. A more
> thorough inspection found antenna 'A' was incorrectly installed on the HF
> output port of the swr/watt meter, instead of the UHF output port. After
> correcting this, the SWR of antenna 'A' was 1.1:1.
>
> Power up of the TE Systems amp was normal and the preamp appeared to
> be working too. Keying the amp and applying 20W of CW drive, the output
> power went to ~300 as normal. But, after releasing the key the IC-736
> returned to receive mode as expected, but the S-Meter displayed >S-10+
> noise. The amplifier power output dropped to 0 as normal, but the amp
> continued to draw 15amps of current. Only after powering off the Astron
> power supply would the amp stop drawing current and IC-736 S-Meter return
> to
> normal levels of noise (S-1 or so).
>
> It appears the amplifier is working as far as power output and
> preamp, but the TX/RX relay and/or RF sense circuitry may be holding the
> amp's bias voltage on and not releasing the amp to RX mode.
> Operating the system into the high SWR due to incorrect placement of
> the antenna on the swr/watt meter may have caused the amplifier to fail.
>
> I have removed the TE Systems amp and Astron power supply from
> service and they are on my workbench at home. The IC-736 is currently
> available to operate 'barefoot' by SARC members.
>
> This seems to be a easy problem to fix and I will keep members
> notified of my findings.
>
> 73
>
> John
> N6VMO
>
>
>
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